Filling PCP Airguns Directly
Filling a PCP airgun directly from a compressor is the most convenient fill method — but there are some things to get right the first time. This guide covers fittings, procedure, and the accessories from AirTanksPlus that make direct fills cleaner and easier.
Direct Fill vs. Tank Fill — What's the Difference?
When you fill a PCP airgun directly, the compressor runs while the gun is connected. Compressed air flows from the compressor, through your filter, through the fill probe or Foster fitting, and directly into the gun's reservoir. When the gun reaches its target fill pressure, you bleed off, disconnect, and you're done.
The alternative is filling an intermediate tank (a carbon fiber or aluminum HPA cylinder) first and then using that tank to fill the gun. The tank-fill method is covered on the Filling Tanks page.
Direct fills are faster per gun if you're only filling one or two. Tank fills are more practical if you're filling multiple guns or shooting on a range where running the compressor isn't practical.
What You Need for a Direct Fill
The Compressor
Your GX Pump CS4-I or equivalent. Make sure it's rated to at least the maximum fill pressure of your airgun. Most PCP airguns run 200–300 bar (2900–4350 PSI). The CS4-I's 400 bar / 5800 PSI ceiling covers everything.
An Inline Filter
Non-negotiable. See the Filters page for a full breakdown. The filter goes between your compressor output and your fill hose — before it ever touches the gun.
The Right Fill Fitting
Most modern PCP airguns use a Foster (female quick-disconnect) fill port. Your compressor output typically terminates in a male Foster or a threaded male fitting. Make sure they match. Some European guns use different thread standards — check your manual.
A Bleed Valve
You need a way to release pressure from the fill hose before disconnecting. Most compressor fill kits include a bleed screw or valve. Always bleed before disconnecting — failing to do this can damage the fill port or blow an O-ring.
AirTanksPlus Accessories for Direct Fills
AirTanksPlus.com is my go-to source for dedicated fill accessories. They stock quality adapters, fill probes, bleed valves, and hose kits specifically designed for PCP fills. The following are worth looking at for direct gun fills.
Note: I link to AirTanksPlus product pages below. These are not affiliate links — I'm sending you there because it's the right product source for this category.
Fill Probe Kits
Some PCP airguns use a fill probe rather than a Foster-style quick disconnect. A fill probe slides into the gun's fill port and seals internally. AirTanksPlus carries probes in the most common diameters. If your gun uses a probe-style fill port, you need the right probe — a Foster fitting won't work.
Check your airgun manual to confirm fill port type before ordering.
Browse AirTanksPlus →Foster Fill Adapters
If your compressor output and your gun's fill port use different thread standards, a Foster adapter bridges the gap. AirTanksPlus carries a range of male and female Foster adapters in both 1/8" BSP and 1/8" NPT threading — the two most common standards on compressors and airguns.
Browse AirTanksPlus →Bleed Valves and Fill Whips
A dedicated fill whip with an integrated bleed valve makes direct fills much cleaner. You connect the whip to your compressor output, connect the other end to your gun, fill, then use the bleed to release pressure before disconnecting. No fumbling with the compressor's built-in bleed — a dedicated fill whip gives you more control at the gun end.
Browse AirTanksPlus →I'll add direct links to specific AirTanksPlus product pages as I confirm what's currently in stock. Their inventory moves around. The base URL is airtanksplus.com.